Translational energy spectra for single-electron capture by O[sup 2+] in He, Ne, and Ar

High-resolution single-electron capture spectra have been obtained for O[sup 2+] ions colliding with He, Ne, and Ar at 4-keV energy. For the He and Ne targets the dominant capture channels involve transitions from the ground [sup 3][ital P] state of O[sup 2+] to the first and second excited states ([sup 2][ital D][sup [ital o]] and [sup 2][ital P][sup [ital o]]) of O[sup +]. Eight well-resolved peaks are observed in each spectrum, corresponding to exactly the same capture channels with the target product ions (He[sup +] and Ne[sup +]) undisturbed in their ground states. One relatively intense peak observed in the Ne spectrum is attributed to capture from the quintet state of O[sup 2+] (2[ital s]2[ital p][sup 3] [sup 5][ital S][sup [ital o]]) to the [sup 4][ital P] state of O[sup +](2[ital s]2[ital p][sup 4] [sup 4][ital P]). The O[sup 2+] in the Ar spectrum exhibits an entirely different character. Eight peaks are discernible, of which five are associated with capture channels which leave the target product Ar[sup +] ion in an excited state. The dominant channel is due to the ground-to-ground transition O[sup 2+]([sup 3][ital P])[r arrow]O[sup +]([sup 4][ital S][sup [ital o]]) with the target Ar[sup +] ion formed in its first excited state (3[ital s]3[ital p][sup 6] [sup 2][ital S]).